The present invention relates to apparatus for use in anchoring systems for mine roof bolts, and the like; more particularly, the invention relates to systems wherein one end of an elongated bolt is anchored in a drill hole by a hardened mixture of resin components originally separated in a two-compartment container. The resin may provide the sole anchoring means, or may be used in combination with a mechanical anchor.
For many years it has been the conventional practice to support and reinforce mine roofs and other rock structures by anchoring a rod or bolt in a drill hole and tensioning the bolt to urge a bearing plate into compressive engagement with a rock formation surface. Virtually all systems for anchoring a mine roof bolt in a bore hole may be classified as mechanical, chemical, or a combination of the two. Most mechanical anchoring systems employ an expansion anchor threadedly engaged with an end portion of the bolt, and including a shell or leaves which are radially expanded into tightly gripping engagement with the drill hole wall in response to rotation of the bolt.
In so-called chemical anchors, some or all of that portion of the bolt or rod within the drill hole is surrounded by a hardened resin grouting material. It has become the usual, if not universal practice to provide such grouting material in the form of a two-compartment package or cartridge wherein a resin and a catalyst are physically separated until the package is broken within the drill hole to permit mixing of the two components. In present formulations, hardening is essentially complete within a few seconds after mixing. The grouting material sets up harder and faster when the components are thoroughly mixed. Many mixing aids have been proposed to assist in fast and complete mixing as the roof bolt is rotated after it is fully inserted in the drill hole to crush the cartridge and release the components.
Although a large number of designs of mechanical expansion anchors have been proposed for use in mine roof support and stabilization applications, virtually all of those in commercial use include a plurality of radially expansible leaves or fingers and a tapered nut, sometimes referred to as a camming plug. The plug has an internally threaded bore which is engaged with a externally threaded end portion of a bolt, whereby rotation of the bolt in the proper direction moves the plug axially on the bolt threads, forcing the leaves or fingers outwardly into tightly gripping engagement with the drill hole wall
The expansion shell, i.e., the leaves or fingers, is held in assembled relation with the plug prior to expansion, and restrained against axial movement as the plug travels down the bolt threads, in one of two ways. In so-called bail type anchors, a metal strap or bail has end portions engaged with the leaves or fingers of the expansion shell and a medial portion passing over the top of the plug. In other anchors, the fingers extend integrally from a ring-like base portion which rests upon a separate support nut threaded on the bolt. The support nut is often in the form of a relatively fragile sheet metal stamping which may be stripped from the bolt threads as downward pressure is exerted on the expansion shell by the camming plug, and thus by the shell on the support nut. In applications employing both chemical and mechanical anchor components, rotation of the bolt to expand the anchor, which typically requires only 2 or 3 seconds, is relied upon to effect mixing of the resin components.
Principal objects of the present invention are to provide a novel article for threaded engagement with a bolt to assist in mixing components of a resin grouting material within a drill hole, and to provide a combined resin-mechanical mine roof bolt anchor having improved resin mixing capabilities.
A further object is to provide an article of manufacture which serves both to support a mine roof expansion anchor shell on a bolt and to aid in efficient mixing of resin components within a drill hole.
Another object is to provide a strippable support nut for an expansion shell with unique structure on the nut for assisting in mixing the components of a resin grouting material as a bolt on which the nut is carried is rotated to expand the shell.
A further object is to provide a combined resin-mechanical roof bolt anchoring system wherein an expansion anchor is fully engaged in a drill hole by rotation of the bolt for the normal amount of time, and the resin components are thoroughly mixed.
Other objects will in part be obvious and in part appear hereinafter.